They rolled their own license but couldn't be bothered to read GitHub's ToS.
"collaborative" license, "opened to the community", "enabling the entire community to participate in its development", "global collaboration" but you have to grant them perpetual rights and waive your own, you're not even allowed to fork lol.
Seems like they're only looking for unpaid workers.
I feel like this whole release is just a PR stunt to remind us that winamp still exists. They don't actually want any help, nor do they want to give anything to the community. They just want to get into gossip, so the spectacular chaos with releasing certificates and 3rd-party proprietary code actually helps for publicity.
The license was always going to be restrictive & focused on what only benefits them as they would never want any clones, etc to be able to make use of it. Also the terms when I look at it from an ex plug-in dev stance seem to prevent any new / updated plug-ins from being built with the plug-in api headers which afaict would fall under their license & surplanting the prior one (no idea if they've changed the in-file stuff or not as I cannot look at their code to avoid issues with work my own player).